To think one could make such a fuss over the palette of a game we've been seeing screen shots of for years is itself curious. It brings back ugly memories of fanboys crying, "Celda!' ... except inverted. Instead of being too colorful, now it's not colorful enough. But complaining about the game's decidedly earth-tone infused aesthetic is akin to criticizing Schindler's List for being black and white ... you're welcome to that opinion, but it's an entirely subjective one devoid of any artistic allowance.
And the engine? Yeah, it's a Gamecube game. It's a Gamecube game running on hardware that is (especially in this case) a Gamecube. If we're going to be criticizing the game for not being made on another platform with superior hardware, then why wasn't Super Mario Bros. made for Super Nintendo ... those graphics were weak, amirite? Why wasn't Gears of War made for Xbox 720 ... it should totally be in virtual reality!
Legible signposts? I shouldn't even address this one. Is it ideal? Maybe not. But on an SD screen, is it really possible or even necessary to be able to read signs from afar? Can any gamer familiar with Zelda's gameplay conceits say this has ever been a deal breaker?
And the fishing? We've only used one rod (you get more later on) in one body of water. Based on earlier experiences playing the game, I had no such problems gauging the surface of the water. The pursuit isn't verisimilitude; this isn't a fishing simulator seeking to faithfully reproduce summers on the lake. It's a minigame; think WarioWare, not Pro Bass Dudes.
To judge a game's worth based simply on the system it's on and the inherent limitations therein suppresses a true appreciation of the entire medium. To extend worn-out movie metaphors to the gaming space: has Star Wars now been obviated that Firefly is out because, after all, the effects were much better, the film stock was clearer, the budget was higher. Do indie films, in their pursuit to deliver unique stories without spending considerable amounts on production, become immediately dismissable because they don't hold up on technological terms with their contemporaries?
In short: sure, Twilight Princess is a Gamecube game that's had Wii controls bolted on it. In our time with the title so far, I remain unconvinced that the Wiimote is the correct controller for this game (the sword swinging still doesn't come naturally). But, like every Zelda game to date, Twilight Princess offers the same brilliant core gameplay mechanics that have driven the series for the last twenty years. Now, the series' dependence on those core gameplay mechanics is another complaint entirely, and one I'd be far more sympathetic too ... even if I wouldn't carry that mantle myself.
[Editorial disclosure: my two cats are named Link and Zelda, so I may not be considered the most neutral party.]